The invention relates to a cylinder head for a plurality of cylinders for a liquid-cooled internal combustion engine, with a configuration for a cooling chamber adjacent to a fire deck, which is divided by an intermediate deck essentially parallel to the fire deck into a lower cooling chamber next to the fire deck, and an upper cooling chamber adjoining the lower one in the direction of the cylinder axis, where the two chambers communicate with each other via at least one flow opening, and where at least one coolant inlet per cylinder, which is preferably located in the fire deck, opens into the lower cooling chamber, and at least one coolant outlet departs from the upper cooling chamber.
In powerful compression-ignition internal combustion engines with strong heat generation, for example, a single continuous cooling chamber for a coolant passing longitudinally through the cylinder head will not provide sufficient cooling of the fire deck. Insufficient heat transfer from the cylinder head, however, may lead to material deformation, leaks and cracking.
In CH 614 995 A a single-cylinder cylinder head for a compression-ignition engine is disclosed, with a lower cooling chamber on the side of the fire deck and an upper cooling chamber, the two cooling chambers being separated by a partition. The coolant is supplied via a feed pipe to annular coolant passages around the valve seats on the one hand, and to the lower cooling chamber on the other hand. From the coolant passages around the valve seats the coolant will flow into a central annular space surrounding a sleeve for a fuel intake device. This is the point from where the coolant will flow into the upper cooling chamber. In this way fire deck and valve seats will be cooled independently. DE 24 60 972 A1 also discloses a single-cylinder cylinder head with two coolant chambers positioned one above the other, which communicate via openings. Such designs are not suitable for engine cylinder heads for a plurality of cylinders, however.
From U.S. Pat. No. 4,304,199 A a cylinder head for a plurality of cylinders for a compression-ignition engine is known, which is provided with a cooling chamber separated by a dividing wall into a lower and an upper part. Upper and lower part are flow-connected by an arcuate opening partially extending along the circumference of the seat of a fuel injector. Via inlet openings in the fire deck the coolant is passed from the cylinder block into the lower part of the cooling chamber, and from there via said arcuate openings into the upper part. The lower part is designed as a continuous space for several adjacent cylinders, so that a longitudinal flow will be generated as well, at least partially. In the instance of strong heat generation in the combustion chamber, it will not be possible to ensure sufficient cooling.
It is the object of the present invention to improve cooling in a cylinder head of the above type, especially in the area of the fire deck.
This object is achieved by associating a lower cooling chamber with each cylinder and by providing that the lower cooling chambers of at least two adjacent cylinders be substantially separated from each other by a partitioning wall and that the upper cooling chamber extend over at least two cylinders. Complete separation of the lower cooling chambers of two adjacent cylinders will prevent a longitudinal coolant flow. The configuration proposed by the invention will also be of advantage for casting. The use of single cores with a compact structure will greatly facilitate the casting of separate lower cooling chambers since there is little danger of distortion. As a consequence, problems with the casting process are minimized.
The coolant will pass through the lower cooling chambers essentially transversally to the cylinder head. This will permit the heat transfer to be precisely defined for each individual cylinder and thus help avoid any influence on cooling performance due to longitudinal coolant flow. In order to avoid vapour lock in the lower cooling chamber when the engine is tilted, it will be of advantage if at least one vent is provided for each cylinder between upper and lower cooling chamber. In this context it is proposed that the vent should be positioned in the area between a longitudinal engine plane and a side-wall of the cylinder head, preferably in a transverse engine plane containing the cylinder axis.
In an enhanced variant of the invention the proposal is put forward that in a cylinder head with at least one fuel injector per cylinder, the intermediate deck be provided with an opening receiving a pipe for insertion of the fuel injector, an annular passage with predefined cross-section being provided between said opening and the pipe, which passage serves as a flow opening between upper and lower cooling chamber.
Alternatively it may be provided that the intermediate deck have a, preferably cast, stub receiving the fuel injector. In order to ensure sufficient coolant supply of the upper cooling chamber, at least one flow opening should be formed by a transfer port in the intermediate deck, and preferably in the area of a side-wall. Significant transverse flow of the coolant in the lower cooling chamber will be obtained by arranging for the inlets and transfer ports to be disposed on opposite side-walls relative to the longitudinal engine plane.
To achieve sufficient cooling of the seat of the fuel injector the lower cooling chamber should preferably surround the fuel injector along its entire circumference in the area of an injector nozzle of the fuel injector opening directly into the combustion chamber.